Conventionally, there has been disclosed a method for correcting a coefficient of a model calculation formula of an intake valve model expressing a relation of an intake pipe pressure at a downstream side of a throttle valve and a cylinder intake air flow rate, based on comparison of an actual measurement value of an operation parameter which is measured during an operation of an internal combustion engine and an estimated value of the operation parameter calculated by using the model calculation formula, in Patent Literature 1, for example. The intake valve model configures a part of an air model for estimating a cylinder filling air amount, and therefore, if the coefficient of the model calculation formula of the intake valve model can be corrected, not only the cylinder intake air flow rate but also the cylinder filling air amount can be estimated with high precision.